A recurring safety problem has been workers falling from the roofs of buildings which are under construction, or on which other work is being performed. Oftentimes, these accidents occur when the workers are moving about and carrying materials back and forth, and it sometimes happens that a worker will simply back over the edge of the roof while not looking.
The magnitude of this hazard has drawn the attention of several regulatory bodies, including the Occupational Safety and Health Administration in the United States, and the Department of Occupational Safety and Health in Canada. As a result, some form of barrier is now required around roof edges where people will be working, and various attempts have been made to comply with this, with very modest success to date. For example, one approach has been to plant a series of posts on the roof and string a cord and warning flags between these; obviously, the actual restraint which is provided by the cord is minimal, and so this must be placed a considerable distance (about 6 feet) inboard from the edge of the roof, which tends to greatly reduce the available working space, and also presents a problem when it becomes necessary to work in the area outside the cord. A somewhat similar approach has involved the use of rails mounted to posts supported by base plates which rest on top of the roof; while this provides a somewhat more positive restraint, the base plates must still be set in a significant distance from the edge of the roof, which restricts the ability of the workers to work near the edge, and this also necessitates a laborious and time consuming effort to move the railings as the work progresses over the surface of the roof.
Attempts have also been made to mount a railing at the very edge of the roof, usually by mounting a plain bracket (such as a conventional leg-and-shield type arrangement) to the outer wall of the building and then mounting the bottom of a stanchion to this so that the stanchion extends up above the edge of the roof and supports railings which are mounted to this. Several problems have been encountered with this approach, and these stem primarily from the inability of this arrangement to withstand any significant loading or impact on the upper railing. Current requirements call for the upper rail to be positioned about 42 inches above the edge of the roof, and OSHA standards require this to be able to withstand the impact of a 200 pound worker, while Canadian standards call for this rail to be able to support a 200 pound static load in either outward or inward directions. When a conventional bracket arrangement is used, these loads translate to a pull-out force on the order of 1000 pounds or more at the wall bracket; for example, if an outwardly directed impact is received by the rail at the upper end of the stanchion, this will tend to force the lower edge of the bracket plate into the wall of the building so that this acts as a pivot point, and this provides a lever arm for pulling out the fasteners which hold the plate to the wall, much in the same manner that a claw hammer provides leverage for removing a nail. Of course, if there is the force at the rail is directed inwardly, the upper edge of the bracket serves as the pivot point, with the same result. Also, because of this pivoting action, essentially the entire pull-out force must be born by whichever fastener is located near the outwardly moving edge of the plate, while the fasteners near the pivot edge bears relatively little of this.
The net result of this situation is that conventional railings of this type are either wholly inadequate in terms of their ability to restrain workers against potential accidents, or they must be constructed so massively as to be very difficult to install and remove, which renders them impractical for many applications. For example, those fasteners which are favored for quick installation and removal from concrete (e.g., those sold under the trade names "Tap-Con" and "Scru-It") simply do not have the load-bearing capacity necessary to withstand the pull-out loads to which they would be subjected in an conventional bracket-mounting arrangement, and so fasteners of a heavier and usually more permanent nature (e.g., lag bolts) must be employed, which simply renders this approach impractical for temporary installations.
Accordingly, there exists a need for a railing system which can be mounted right at the edge of a roof so as to make the maximum space available for work, and also eliminate the need to move this as the work progresses. Furthermore, there exists a need for a railing system of this type which is easily installed and removed, so that this can be efficiently used on a temporary basis during building construction. Still further, there is a need for a railing system of this type which is economical to fabricate, and which takes advantage of readily available railing members, such as standard length 2.times.4s.